Do you have children? If not, you do not even know the love of a child from a parent/mom. The birth, love and care. If you do have children, their are other family members to a male spouse who you love. Not just a gf or a wife. Their is a reason someone whould say something mean to a gf/wife. Is that gf/wife only thinking of her feelings and what she wants or does she think about all pieces of a family?
You will walk in your mother in laws shoes one day, if you have children. If not then you may not ever understand the love of child from a parents point of view.